The invention relates to a method for obtaining PWM values for an LED module having n LED chips from various color ranges, wherein n>1, wherein a PWM (=pulse width modulation) value is obtained for each LED chip to generate a target color value.
In general, LEDs comprise a plurality of LED chips, and are distinguished by a long service life, great robustness, low energy consumption and a small constructive form, which result in a large number of possibilities for utilization, for example in entertainment electronics, medical technology, telecommunication and in the automotive field. The n LED chips may be applied directly to the circuit board (COB, chip on board), accommodated in a common LED housing (multicolor LED), or accommodated in separate housings (single color LED).
Through additive color mixing on the basis of RGB technology, using LED modules that comprise red, green and blue chips, nearly any mixed color (target color) can be realized. This is done through pulse width modulation, by obtaining a PWM value for a particular target color of each LED chip, which is a measure of the electric current flow through the respective LED chip. A PWM value is the duty cycle (pulse width per cycle duration). In this way the brightnesses of the LED chips, and thus the contribution of the individual LED chips to the mixed color, can be influenced.
An exact color mixture is difficult, however, since the sorting of the LED chips of a color according to a standard includes a large brightness and color range, and both the brightness and the color value are dependent on current and temperature. Different mixed colors therefore result at different temperatures.
While it is possible in principle to perform a corresponding correction of the PWM values, exact calculation of the appropriate PWM values would be extremely computation-intensive and could not be realized using an economical processor.
For economical products, the color changes due to temperature and current are therefore accepted, although this results in products of lower quality.